Method and apparatus for determining the total carbon content of aqueous systems



J. L. TEAL ET AL METHOD AND APPARATUS FOR DETERMINING THE Jan. 3, 1967TOTAL CARBON CONTENT OF AQUEOUS SYSTEMS Filed July 6, 1964 United StatesPatent Ofifice 3,296,435 Patented Jan. 3, 1967 METuon AND APPAnATUs nonDETERMINING THE TOTAL CARBON CONTENT OF AQUEOUS SYSTEMS James L. Teal,Clayton E. Van Hall, and Vernon A. Stenger, Midland, Mich., and John W.Safranko, Rancho Cordova, Calif assignors to The Dow Chemical Company,Midland, Mich, a corporation of Delaware Filed July 6, 1964, Ser. No.380,597 Claims. (Cl. 250-435) This is a continuation-in-part applicationof US. Serial No. 232,107, filed October 22, 1962, now abandoned.

The present invention concerns a novel analytical method and apparatusfor determining the carbon content of aqueous systems containing smallamounts of dissolved or highly dispersed carbonaceous materials.

Accepted methods for analyzing aqueous systems for carbonaceous ororganic materials are generally based upon wet oxidation techniques,i.e., using chemical reagents at moderate temperatures; The amount ofcarbonaceous material is determined by the amount of oxidant consumedwhich may be found volumetrically or photometrically, or is determinedby the quantity of carbon dioxide evolved which may be found bymanometric, gravimetric or alkalimetric procedures. In addition, thermalconductivity and mass spectrometry have been utilized to determine thecarbon dioxide. These methods, though some are widely used, suifer fromthe variable susceptibility of organic compounds to oxidation bycommonly used reagents such as chromic acid, the interference ofchloride and other ions and the length of time required to complete theanalysis.

Increasing concern with the problem of water pollution and wastetreatment has brought about a need for a rapid and precise method fordetermining carbonaceous matter in aqueous systems. The advantages ofrapid analytical methods permitting immediate evaluation of correctivetreatments at water pollution sources are manifest.

It is an object of the present invention to provide a rapid analyticalmethod for determining the total carbon content of aqueous systemscontaining small amounts of highly dispersed carbonaceous matter, i.e.,homogeneous aqueous dispersions or solutions of carbonaceous solids orliquids. The total carbon content of such a system is a convenientindicator of the total carbonaceous matter therein. Particularly, it isan object to provide an analytical method effective regardless ofwhether the carbonaceous matter is present in the form of a truesolution, or as a homogeneous dispersion of finely divided solidparticles. An additional object is to provide a highly accurate andreproducible analytical method conveniently adaptable for waterpollution control purposes. A further object is to provide an apparatusfor carrying out the aforedescribed analytical method. Other objectswill become apparent hereinafter as the invention is more fullydescribed.

In accordance with the invention, an analytical method is providedwhereby the total carbon content of an aqueous system containingcarbonaceous matter is determined with an accuracy of plus or minus afew parts per million. The analytical method comprises the followingoperations. A stream of oxygen is passed, at a constant rate, through aheated zone within a combustion conduit. Contained within the heatedzone of the conduit and disposed transversely across the same is aporous, gas-permeable diffusing member of a material essentiallychemically inert to oxygen and steam at an elevatedcombustion-supporting temperature, e.g., 900 C. The diffusing member ispositioned within the heated zone of the combustion conduit at somedistance from the oxygen inlet end of the heated zone sufiicient todefine, in conjunction with the conduit, a sample expansion zone.Usually, it is positioned at least about /5 of the distance through theheated zone as measured from the oxygen inlet end thereof. Preferably,it is positioned about /2 to A of the way through the heated zone. By sopositioning the diffusing member, which may be otherwise termed agas-permeable, diffusing plug, there is provided a sample expansion zonein which a substantial blanket of oxygen is maintained upstream from thediffusing member and within the heated zone of the combustion conduitduring operation of the apparatus. Upon injection of the test sample ofthe aqueous system to be analyzed, the sample is vaporized and for aninstant some back pressure is generated. The volume of the sampleexpansion zone is adequate when the formation of condensate in the inletoxygen stream or other cool zones upstream from, and communicating with,the heated zone is avoided.

Having established the oxygen stream at a predetermined, constant rateof flow (predetermined means at a preset levelknowledge of absolute flowrates is not necessary) and brought the heated zone of the combustionconduit to a suitable combustion temperature, i.e., at least about 700C., preferably about 900 C., but below about 1,l00 C., a small amount ofan aqueous system containing a small proportion of highly dispersedcarbonaceous matter is rapidly injected into the heated zone of thecombustion conduit on the upstream side of the diffusing mem ber. Whilethe oxygen stream preferably consists of pure oxygen, gaseous diluents,substantially free of carbonaceous materials, such as nitrogen, oxygen,helium and the like, can be tolerated as components of the oxygenstream. Best results are obtained if the sample is rapidly injected intothe heated zone in a direction parallel, or practically parallel, to thelongitudinal axis of the combus tion conduit. When the combustionconduit is aligned vertically, rapid injection of the sample can beachieved by dropping it into the combustion zone. In any event, thesample is deposited within the heated zone of the com bustion conduit ata point which is some distance from the oxygen inlet end of the heatedzone.

When the line of injection is essentially parallel to the longitudinalaxis of the combustion conduit, rapid injection techniques Will depositthe aqueous sample within the heated zone at or near the diffusingmember. Thus, by virtue of the position of the diffusing member there isa cushioning oxygen blanket on the upstream side of the gasifiedinjected sample which aids in preventing back flow of the resultinggaseous product out of the heated zone. The steam and vaporizedcarbonaceous matter, which are produced substantially instantaneouslyupon injection of the sample, are subsequently swept through theremainder of the heating zone and the diffusing member into a confinedcooling zone.

While there is undoubtedly some oxidation of the carbonaceous matterpresent in the sample upon vaporization thereof, it is essential forcomplete and reproducible combustion that the gasified sample passthrough the diffusing member. It insures retention of the gaseousproduct Within the heated zone long enough to achieve completecombustion and provides a reservoir of both heat and oxygen to completethe oxidation of any carbonaceous matter present.

Within the cooling zone following the heating zone, the gaseous productfrom the heating zone is usually cooled to a temperature at or belowthat of the apparatus subsequently used for detecting the carbondioxide. This is done to avoid the build-up of condensate in thedetector. Normally, the gaseous product will be reduced to about normalroom temperatures. As the gases cool, water vapor condenses and isthereby effectively separated from the gas stream to be analyzed. Suchcondensate is usually collected in a water trap from which accumulatedwater can be intermittently with-drawn. While uniform cooling of thegaseous product and thus consistent separation of condensate from thecooled gases are desirable for optimum operation, good results can alsobe achieved by operating with only minimal cooling of the gaseousproduct such as would occur incidentally while conveying the gases intothe analyzer through aircooled tubing.

After flowing through the cooling zone, the cooled gaseous productpasses into an analyzer for quantitatively determining its carbondioxide content. Preferably, an analyzer is used which provides a signalin the form of electrical voltage, the strength of which is proportionalto the concentration of carbon dioxide in the eflluent gases.

A particular, and preferred, analyzer is a non-dispersive type, infraredanalyzer sensitized for carbon dioxide analysis. The construction ofthese analyzers and the manner in which they are operated are describedin such references as United States Patents 2,698,390, 2,681,415, and2,709,751.

The voltage signal output from such carbon dioxide analyzer is adaptedby suitable amplifiers, e.g., that described in U.S. Patent 2,413,788,and graphic recorders to provide readings which can be converted to, orread directly as, carbon dioxide concentrations in the sample byreference to standard calibration curves prepared by analyzing knownsamples under comparable operating conditions. To provide comparableanalytical readings for such purposes, care must be exercised to insurethat sample volume, amplifier gain and recorder voltage range settingsare at predetermined identical values and further that the temperatureand the oxygen flow rates employed during the analytical operations areidentical, or at least above minimum operational levels at which theanalytical results become independent of these variables.

In a preferred embodiment wherein analytical results are obtained as acurve whose amplitude is a function of carbon dioxide concentration inthe gaseous product, the actual carbon content of the aqueous systemtested is correlated with the maximum amplitude, or peak, of the curve.Having previously calibrated such readings, direct readings of the peakordinants give the carbon concentration in the aqueous system tested.

It will be recognized that the above-described procedure providesinformation with regard to the total carbon content of aqueous systemsinclusive of carbon present in inorganic as well as organic forms.However, for most aqueous systems the actual organic carbon content canbe approximated by first treating the sample to be analyzed to removeany inorganic carbon (carbonate) therein. This is accomplished byacidifying the sample with a mineral acid of sufficient strength toliberate any carbonates present as carbon dioxide and thereafter blowingthe sample with a carbon dioxide-free, inert gas.

A major problem involved in the development of the aforedescribedprocess was the relatively large volume of steam produced when water isplaced in the heating zone. As calculated from ideal gas behavior, onemilliliter of water yields 5.6 liters of steam at 950 C. The

great expansion of a sample on vaporization causes the gas produced toblow through the combustion conduit with high velocity making completeand reproducible oxidation difiicult. In order to obtain complete andreproducible oxidation of organic matter contained in the aqueous sampleunder these conditions, it was found to be essential to employ smallsamples of the aqueous system to be tested and to have a diffusingmember suitably placed in the heated zone of the combustion conduit. Inthis connection, it 'has been found desirable to maintain the volume ofthe aqueous test sample within the range from about 0.005 to about 0.5percent, preferably 0.01 to 0.1 percent, of the bed volume. By bedvolume is meant the total volume of the heated zone within thecombustion conduit. For best results, the heated zone bed volumes aremaintained within the range from about 20 to 200 cubic centimeters,While bed volumes of 40 to cubic centimeters are preferred. Along withthe heated zone bed volume, it is desirable to control the crosssectional area of the combustion conduit. For a cylindrical combustionconduit, the maximum diameter permissible is about 3 centimeters.Preferably, the maximum diameter is kept below about 2 centimeters. Inany event, the combustion conduit should not have a cross sectional areaexceeding about 7 square centimeters. The smallest cross sectional areapermissible is that which will just allow for rapid expansion of theaqueous test sample without consequential rupturing of the combustionconduit.

While the quantity of carbonaceous matter contained in the aqueous testsample is small, e.g., from a few parts up to as much as 500 parts permillion, and not much oxygen is required for its complete oxidation, itis nevertheless essential to provide ample opportunity for contactbetween the carbonaceous matter and oxygen. This is accomplished by theprovision of the diffusing member. Even though the bulk of the oxygenatmosphere in the combustion conduit is replaced by steam uponvaporization of the test sample, the diffusing member containssufficient oxygen usually in an adsorbed condition, and stored heat topromote complete oxidation of the carbonaceous matter in the testsample.

In addition to meeting the foregoing requirements, diffusing membersemployed herein must be sufficiently permeable to gases in order toprevent the creation of excessive back pressures upon vaporization ofthe aqueous test samples. To provide an effective balance between theconflicting requirements of low resistance to gas flow over and againstthe requirement for providing sufiicient oxygen and heat to completeoxidation of injected carbon-aceous matter, it has been found desirableto utilize diffusing members, i.e., gas-permeable, diffusing plugsfilling the combustion conduit, at least 0.5 centimeter long with amaximum limit of about 10 centimeters. Preferably, the diffusing memberis from 1 to 4 centimeters long and is constructed of a compactedfibrous or granular mate rial essentially chemically inert to oxygen andsteam. Essentially chemically inert means the material adopts anessentially constant chemical consistency upon ex'- posure to steam andoxygen, at an elevated combustion supporting temperature, except that itis contemplated herein that the surface of such material may adsorb ordesorb gases such as oxygen. Suitable materials of construction for thediffusing member include quartz wool, quartz chips, sand, pumice, andthe like siliceous materials. Also suitable are finely dividedtransition metals, e.g., nickel, chrome, manganese and platinum, andtransition metal oxides, e.g., copper, cobalt, manganese, vanadium,cerium and thorium oxides, employed either alone or on inert supportsurfaces. Preferred for this use is fibrous asbestos which may be, ifdesired, coated with an oxide of a transition metal. Cobalt oxide iseflicient in the presence of steam. Since the oxidation must take placeso rapidly, a platinum gauze downstream in the heated zone from thediffusing member in the heated zone may also be used to insure completeand reproducible oxidation.

It is to be noted that the situation encountered herein is quitedifferent from that involved in ordinary microcombustion techniqueswherein complete oxidation of the sample to be analyzed is accomplishedover an extended period in a slow stream of oxygen.

Typical apparatus for carrying out the above-described analyticalprocess is illustrated in the accompanying drawings. FIGURE 1 is aschematic drawing of a complete apparatus suitable for accomplishing theanalysis of dilute aqueous systems of carbonaceous materials for carboncontent in accordance with the invention. FIGURE 2 shows the generalconfiguration of a representative combustion conduit containing adiffusing member and an optional platinum gauze.

The apparatus illustrated in FIGURE 1 comprises oxygen supply means 2,sample injection means 3, heating means 4, in which there is situated acombustion conduit 22, cooling means 5, condensate removal means 6integral with the cooling means 5, and carbon dioxide detection means 7.More particularly, there is shown in the illustrated preferredembodiment regulated oxygen supply means 2 which comprises an oxygentank 11 for feeding oxygen to the combustion conduit 22 through oxygenflow control means 8, which in the illustrated embodiment consists of aseries arrangement of a pressure regulator 12, valve 13, flow meter 14,and back flow check valve 15. These elements ofth-e apparatus areoperatively coupled in the order specified with suitable interconnectingconduits 16, 17, 18, 19 and 20, respectively. Subsequent to the checkvalve 15, the oxygen stream is introduced into the inlet end of thecombustion conduit 22, which is adapted at the oxygen inlet end toreceive sample injection means 3, such as the illustrated syringe 23.

The combustion conduit 22 has a heating zone 21 situated within theheating means 4, which, in the illustration, is an electric muffiefurnace 24. This furnace is regulated by means of a variable powercontrol 26. Temperature readings within the heating means 4, if desired,can be obtained by means of a pyrometer 27.

Gaseous products from the heating zone 21 of the combustion conduit 22are passed through cooling means 5, which, in the illustrated preferredembodiment, consists of a water-cooled condenser 28 in series withcondensate removal means 6 and an optional gas filter 30. The specificcondensate removal means 6 illustrated consists of a U-shaped condensatetrap 29 adapted with a stopcock 31 for intermittent water drainage. Thewatercooled condenser 28 is coupled directly to the outlet or dischargeend of the combustion conduit 22 and it discharges directly into thecondensate trap 29. Interconnecting conduits 32 and 33 thereafterconduct the gaseous product through the gas filter and thence intocarbon dioxide detection means 7.

The carbon dioxide detection means shown in FIG- URE 1 consists of anelectrically interconnected association of. a non-dispersive,carbon-diomde-sensitized, infrared analyzer 35 which produces a variablevoltage signal to be amplified by means of a low voltage amplifier 38.The enhanced electrical signal is then fed into a continuous graphicrecorder 39, which produces a curve 41 on a continuous strip of paper42. The amplitude of, or the area under, the curve 41 is a function ofthe carbon dioxide concentration in the detection cell 36 of the infrared analyzer 35. After passing through the detection cell 36 thegaseous product is discharged to the atmosphere through a vent 37.Essential controls in the detection means 7 are the amplifier gaincontrol 43 and the recording voltage range control 44.

!III FIGURE 2, a representative combustion conduit 50 is shown in moredetail. It consists of two separable parts which are an oxygen inlet 54and a cylindrical combustion tube 51. Seated within the oxygen inlet 54is an injection tube 52 adapted to receive injection means in the formof a syringe. The injection tube 52 is aligned in a directionessentially parallel to the longitudinal axis of the combustion tube 51.The oxygen inlet 54 is coupled with the cylindrical combustion tube 51by means of a ground glass joint 53. Within the cylindrical combustiontube 51 is a diffusing member 55. Subsequent thereto in the direction ofthe oxygen stream is an optional platinum gauze 56. Between thediffusing member 55 and the platinum gauze 56 is a small retainingindentation 60 in the cylindrical combustion tube 51. This provides aretaining seat for the difiusing member 55. Each end of the assembledcombustion conduit 50 is adapted for coupling with preceding andsucceeding apparatus elements. The upstream oxygen inlet is a smalltubular nipple 58 and and the downstream outlet, coupling means is aball portion 57 of a ball joint.

While certain preferred embodiments of the abovedescribed fundamentalapparatus components have been set forth, numerous alternatives willoccur to those skilled in the art. For instance, with regard to oxygensupply means 2, it is only necessary that there be provided a confinedstream of oxygen subject to precise flow rate control. Knowledge of theactual flow rate is not necessary, however, so long as the oxygen flowrate can be controlled to a predetermined and constant rate. To this endany combination of mechanical means for supplying and regulating anoxygen stream can be used in place of that illustrated. Insofar asheating means 4 is concerned, apparatus capable of providing controlledheating over a temperature range of 700 to 1,100 C. can be used. Whilean electric resistance furnace is efiicient for this purpose, inductionheating means, or any other convenient heating means, can be used.Similarly, sample injection means 3 can be provided by any mechanicalapparatus capable of supplying measured aliquots of aqueous systems andrapidly injecting them into the heating zone 21 of the combustionconduit 22. For example, direct insertion of the aqueous sample to beanalyzed into the heating zone 21 can be accomplished by oxygen drivensprayers adapted to provide controlled amounts of spray. Cooling ofgaseous products from the heating zone 21 can be accomplished in aconventional manner such as by passing them through the describedwater-cooled condenser 28. Alternately, air-cooled condenser, which maybe simply the coupling tubing between the combustion conduit and theanalyzer, are also effective for this purpose. While it is not necessaryin every case, it is preferred to employ a gas filter 30 which willseparate any particles or moisture entrained in the gaseous productprior to its introduction into the detection cell 36. While theparticular carbon dioxide detection means 7 described above ispreferred, any analytical apparatus capable of indicating the quantityof carbon dioxide in the gaseous product with desired sensitviity andspecificity can be used.

Materials of construction employed in the above combustion gas trainmust generally meet the criteria of having resistance to oxygen andmoisture. Moreover, it is desirable, at least in the gaseous producttrain, that materials of construction be essentially non-adsorbents forcarbon dioxide. Within the combustion zone itself, it is necessary thatthe materials of construction be inert to oxygen and steam at theelevated temperatures used for combustion. Such materials include, forexample, fused silica, Vycor glass, glazed ceramics and the likesiliceous materials.

In a specific embodiment of the abovedescribed apparatus shown in FIGURE1, inch gum rubber tubing was utilized to provide the connectingconduits 16, 17, 18, 19 and 20. The oxygen stream pressure regulator 12was a Watts Regulator Type 26 Model M1 and the valve 13 consisted of aHoke needle valve. A combination of a precision sapphire ball within aFisher-Porter Flow Metering Tube 08F-1/ 16-20-4/ 74 served as the flowmeter 14. Serving as the check valve 15 was a Kimble Valve No. 38006.Combustion supporting temperatures were generated within the combustionconduit 22 with an electric mufile furnace 24 operating on a voltage of120 volts and a maximum power consumption of 700 watts. The powercontrol 26 was a Powerstat variable voltage transformer.

A cylindrical combustion tube 51 consisting of fused silica and havingan inside diameter of 1.27 centimeters and a length of about 30centimeters was used in the constr'uction of the heated zone 21 of thecombustion conduit 50. An oxygen inlet 54 was provided in the form of atubular glass T, with the cross bar of the T having a Vycor ground glassjoint 53 at one end for coupling with the fused silica combustion tube51 and a No. 18 stainless steel syringe needle 52 about 5.2 centimeterslong seated in the opposite end of the cross bar as receiving means forsample injection means in the form of a syringe. When the components ofthe combustion conduit 50 were assembled, the needle 52 was directed ina line essentially parallel with the longitudinal axis of thecombustiontube 51. The stem of the tubular glass T provided a nipple 58 forconnection with the 3/ 16 inch gum rubber interconnecting conduit 20. AHamilton No. 705N syringe 23 was employed as the injection means 3.

Within the combustion tube 51 at about 22 centimeters from the inlet endthereof was placed a diffusing member 55 about 4 centimeters longconstructed of ignited asbestos fibers. The diffusing member was formedby gently tarnping the fibers into place against a retaining indentation60 within the combustion tube 51 with a glass rod. A platinum gauze 56about 10 centimeters long was placed just behind the diflusing member55. After assembling its component parts, the combustion conduit 50 wasplaced within the electric mufile furnace 24 so that the tip of thesyringe needle 52 was just outside the heating zone of the furnace 24but yet in position such that, upon injection of the aqueous sample, thefull amount thereof was deposited within the heating zone 21 of thecombustion conduit 22.

The gaseous products produced upon injection of a test sample wereconducted through a gas train consisting of a series arrangement of awater-cooled condenser 28, a U-shaped water trap 29 and a gas filter 30containing a 10-13 micron filtering element. The water trap 29 wasadapted for intermittent drainage of accumulated water by means of astopcock 31. The interconnecting conduits 32 and 33 consisted of inchgum rubber tubing.

Carbon dioxide detection means 7 employed with the foregoing apparatusconsisted of an infrared analyzer 35 (Beckman Model 21A) equipped with a13.3 centimeter detection cell 36 sensitized for analysis of carbondioxide. The detection cell 36 was maintained at a temperature of 45 C.to prevent the formation of condensate which would interfere with theaccuracy of the analytical result. Output from the analyzer 35 was fedby electrical leads 63 and 64 to a low voltage amplifier 38.Subsequently, the amplified output of the analyzer was fed into agraphic recorder 39 (Sargent Model MR) through electrical leads 61 and62. The recorder 39 was set by the voltage recording range control 44 tooperate in the -5 millivolt range. The gain control 43 of the amplifier38 was set at a predetermined level to provide a desired response in therecorder 39.

To carry out the described analytical technique, it is necessary toselect a suitable sample size which may be as little as about 1microliter up to as much as l milliliter, depending upon the bed volumeof the combustion conduit 22. A preferred sample size is within therange from to 100 microliters. To begin a particular analysis, theheating means 4 is turned on and brought to a temperature within therange from about 700 to about 1,100 C., preferably about 900 to 1,000 C.Oxygen is also turned on and the flow rate adjusted to a desiredconstant level so as to provide from about 0.2 to about 4, preferably0.7 to 1.5, heated bed volumes thereof per minute. Depending on the sizeof the heated bed volume, the oxygen flow rate can be within the rangefrom as little as 10 to 800 cubic centimeters (S.T.P.) per minute.

It is to be noted that the best oxygen flow rates will depend somewhatupon the heating zone 21 bed volume. For instance, small bed volumeswith high oxygen flow rates or large bed volumes with oxygen flow ratesthat are too low will tend to engender erratic combustion with possiblecountercurrent diffusion of the combustion gases, such that theanalytical results will tend to show poor reproducibility. Also, in thisconnection, it is to be pointed out that while integration calculationscan be used to correlate the recorded signal with actual total carboncontents, the most convenient and rapid evaluation of the recordedsignal is made by considering only the amplitude (peak height) of therecording curve. To obtain well defined amplitude, or sharp peaks, bedvolume and oxygen flow rate conditions should be adjusted within theabove-described limits in order to produce curves having amplitudes welldefined within a relatively short period, e.g., from a little as 5seconds up to no more than about 1 minute. For this purpose, severaltrial runs utilizing varying oxygen flow rates with a given combustionconduit 22 will provide basis for the selection of efficacious oxygenflow rates.

After the oxygen flow rate, temperature of the heating means 4 andcarbon dioxide detecting means 7 have achieved operating readiness, aselected sample of the aqueous system to be analyzed is rapidly injectedinto the heating zone 21 of the combustion conduit 50 with the syringe23. Within a short time, the continuous graphic recorder 39 will producea curve 41 whose amplitude may be read directly in terms of the totalcarbon content of the sample tested or may be correlated with the totalcarbon content by reference to a standard calibration curve of curveamplitudes plotted against to tal carbon of previously analyzed knownsamples. Such standard calibration curves can be obtained for knownaqueous systems containing a high purity organic material such asglacial acetic acid under operating conditions such that comparableanalytical results are obtained.

For a given apparatus setup, simple test operations according to theprocedure outlined above can be employed to determine optimum operatingconditions within the aforedescribed operational limits. For thegreatest reproducibility with the specific apparatus described above, itis desirable that oxygen flow rates be above a certain minimum, i.e.,above about 40 cubic centimeters per minute but not more than about 200cubic centimeters per minute, and that the quantity of carbonaceousmaterials present in the sample to be analyzed be within the range fromabout 5 to 150 parts per million. Within these operational levels, theresults achieved are independent of variations in the parametersspecified. However, it is preferred to establish optimum operatingconditions and maintain such during all operations.

Numerous tests have been made on aqueous systems containing knownamounts of car-bon. In such operations small amounts of a carbonaceousmaterial, such as those specified below, were added to deionized waterto provide a predetermined proportion of carbon in parts per million.Four analyses of each standard solution were made using an apparatuslike that described above. The results were statistically averaged todetermine the percentage recovery, i.e., times the carbon found, dividedby the carbon calculated to be present. The sample size used was 20microliters and the temperature within the furnace was 950 C. Oxygen waspassed into the combus tion tube at a constant rate of 50 cubiccentimeters (S.T.P.) per minute. The systems analyzed and the resultsobtained are set forth in the following table.

member at a distance into the heated zone from the inlet end thereofsufiicient to define, in conjunction TABLE I.ANALYSES OF KNOWN SOLUTIONSCarbon in Parts Per Million Std. Avg. Solute Found Dev. PercentCalculated Recovery Max. Min. Avg

Benzoic acitL 68. 8 69. 67. 4 68.2 0.66 99.1 en 70. 6 77. 2 76. 76. 9 0.100. 4 bucrose 104. 8 105.1 104. 3 104. 5 0. 99. 7 Glycine-" 100. 7 101.2 99. 5 100. 3 0. 69 99. 6 Pyridine.. 1 5.6 104. 4 103. 6 104. 2 0.4098. 7 Urea 100.0 100. 9 99. 1 99. 8 0. 80 99. 8 Sodium cyanide. 122. 5122. 1 119. 5 120. 5 1. ll 98. 4 Acetanilideuu 75. 4 76.0 75.0 75.4 0.48 100.0 pnitroaniline 106. 2 105. 8 104. 9 105. 4 0. 52 99. 24-arninoantipyr 111. 5 110. 6 108. 9 110.2 0. 85 98.8 Sulfanilic acid.89. 3 90. 5 88.6 89. 3 0. 90 100. 0 Diphenylamine 87. 8 87. 6 86. 8 87.40. 40 99. 5 dl-methioniue 103. 0 102. 7 101.8 102. 5 0. 99. 52,4,6-triehlorophenoL- 75. 4 76. O 74. 0 75. 0 0. 84 99. 5 Sodiumcarbonate 99. 5 100.0 99. 2 99. 4 0.40 99. 9 Acetic acid in 20% NaCl100. 0 101. 0 99. 0 100.0 0.82 100. 0 Acetic acid in 20% 03.01 100. 0100. 0 98. 1 99.1 0.78 99. 1

1 All results are based on 4 determinations. Calibrations were made withstandard solutions of acetic acid in Water.

For subsequent operations with aqueous systems of unknown quantities ofcarbonaceous materials, a standard calibration curve was made byanalyzing known solutions of glacial acetic acid. The analyticaloperations were carried out as described above. Having prepared astandardization curve with the accumulated data whereby the recordedpeak height could be correlated with the carbon content of the aqueoussystem being tested, subsequent determinations were made on unknownsolutions in a like manner. Data accumulated in several runs withparticular unknowns indicated highly reproducible analyses with astandard deviation of only plus or minus one part per million or onepercent at the 100-part per million level.

While the foregoing illustrations deal chiefly with true solutions ofcarbonaceous materials, aqueous systems which comprise dispersions offinely divided solids are also efficiently analyzed for total carboncontent in accordance with the method of the invention. It is onlynecessary in such instances that care should be exercised to insure thatrepresentative samples are obtained for analysis. Thus, in someinstances it may be desirable to subject the aqueous system to beanalyzed to shearing agitation in order to break down agglomerates intoparticle sizes within the capability of the injection means used. Inother instances it may be necessary to filter out rough or comparativelylarge particles in order to avoid plugging of the injection means. Ingeneral, any aqueous system containing a small amount of highlydispersed carbonaceous matter can be analyzed regardless of whether thecarbonaceous matter is dissolved or suspended.

While it is preferred in the interest of obtaining reproducible resultsto analyze aqueous systems containing no more than about 500 parts permillion of highly dispersed carbonaceous material, it is possible toanalyze aqueous systems with greater proportions of carbonaceousmaterial by diluting representative samples thereof to appropriateconcentration levels.

What is claimed is:

1. A method for rapidly determining the total carbon content of anaqueous system containing a small amount of highly dispersedcarbonaceous matter which method comprises (1) passing a continuousstream of oxygen at a constant fiow rate through a combustion conduithaving a heated zone at a temperature within the range from about 700 toabout l,l00 C., within which heated zone there is positioned agas-permeable difiusing with the combustion conduit, a sample expansionzone within the heated zone of adequate volume to avoid the formation ofcondensate upstream from the heated zone, said difiusing member being ofa material which is essentially chemically inert to oxygen and steam atthe temperature of the heated zone;

(2) rapidly injecting a small predetermined amount of the aqueous systemto be analyzed into the oxygen stream within the heated zone of thecombustion conduit on the upstream side of the diffusing member;

(3) sweeping the gaseous product formed in the heated zone through thediffusing member and into a cooling zone by continuing the oxygen streamat the aforesaid constant flow rate whereby the gaseous product iscooled;

(4) thence sweeping the cooled gaseous product into an analyzer forquantitatively indicating the carbon dioxide in the gaseous product.

2. A method for rapidly determining the total carbon content of anaqueous system containing a small amount of highly dispersedcarbonaceous matter which method comprises:

(1) passing a continuous stream of oxygen at a constant flow ratethrough a combustion conduit, said combustion conduit having a maximumcross-sectional area of about 7 square centimeters and a heated zonewith a volume within the range from about 20 to about 200 cubiccentimeters maintained at a combustion supporting temperature within therange from about 700 to about 1,100 C., within which heated zone thereis a gas-permeable diffusing memher at least about 0.5 centimeter longof a material, which is essentially chemically inert in the presence ofoxygen and steam at the temperature of the heated zone, said ditfusingmember being positioned wtihin the combustion conduit at least about /5of the distance through the heated zone as measured from the oxygeninlet end thereof;

(2) rapidly injecting a small predetermined amount of the aqueous systemto be analyzed into the oxygen stream within the heated zone of thecombustion conduit on the upstream side of the diffusing member;

(3) sweeping the gaseous product formed in the heated zone through thediffusing member and into a cooling zone by continuing the oxygen streamwhereby the temperature of the gaseous product is lowered;

(4) thence sweeping the cooled gaseous product into an analyzer forquantitatively indicating the carbon dioxide in the gaseous product.

3. A method as in claim 2 wherein:

(1) the aqueous system to be analyzed contains from about 2 to about 500parts per million of highly dispersed carbonaceous matter;

(2) the oxygen flow rate is within the range from about 1 to about 4times the bed volume of the heated zone per minute; and

(3) the volume of the sample of the aqueous system to he analyzed isfrom about 0.005 to about 0.5 percent of the bed volume of the heatedzone.

4. A method as in claim 2 wherein the aqueous system to be analyzed israpidly injected into the oxygen stream within the heated zone in adirection essentially parallel to the longitudinal axis of thecombustion conduit.

5. A method for rapidly determining the total carbon content of anaqueous system containing a small amount of highly dispersedcarbonaceous matter which method comprises:

(1) passing a continuous stream of oxygen at a constant andpredetermined flow rate through a combustion conduit, said combustionconduit having a maximum cross-sectional area of about 7 squarecentimeters and a heated zone with a volume within the range from about20 to about 200 cubic centimeters maintained at a combustion supportingtemperature within the range from about 700 to about 1,100 C., in whichheated zone there is a gas-permeable diffusing member at least about 0.5centimeter long of a material, which is essentially chemically inert inthe presence of oxygen and steam at the temperature of the heated zone,said diffusing member being positioned within the combustion conduit atleast about of the distance through the heated zone, as measured fromthe oxygen inlet end thereof;

(2) rapidly injecting a small predetermined amount of the aqueous systemto be analyzed in the oxygen stream within the heated zone of thecombustion conduit on the upstream side of the diffusing member;

(3) sweeping the gaseous product formed in the heated zone through thediffusing member and into a cooling zone by continuing the oxygen streamat the aforesaid constant rate whereby the temperature of the gaseousproduct is lowered;

(4) thence sweeping the cooled gaseous product into an analyzer whichproduces an electrical voltage proportional to the carbon dioxide in thegaseous prtduct, which electrical voltage is fed to a recorder; an

(5) calibrating the recorded indicia of the carbon dioxide concentrationin the gaseous product against data obtained by analyzing aqueoussystems containing known amounts of a carbonaceous material undercomparable operating conditions, whereby the carbon content of theaqueous system is determined. 6. An apparatus for determining the totalcarbon content of an aqueous system containing a small amount of highlydispersed carbonaceous 'matter, which apparatus comprises:

(1) oxygen fiow control means for maintaining a confined continuousoxygen stream from a pressurized source of supply at a constant andpredetermined rate;

(2) a combustion conduit having an inlet and an outlet, said combustionconduit being coupled at the inlet to the oxygen flow control means andhaving a heating zone in which there is a gas-permeable diffusing memberof a material which is essentially chemically inert to oxygen and steamat combustion supporting temperatures, said diffusing member beingpositioned Within the heating zone of the combustion conduit at adistance from the inlet thereof sufficient to define in conjunction withthe combustion conduit 21 sample expansion zone of adequate volume toavoid the formation of condensate upstream from the heating zone, andsaid combustion conduit being adapted at the oxygen inlet end thereof toreceive sample injection means for rapidly injecting a smallpredetermined amount of the aqueous system to be analyzed into theheating zone;

(a) heating means in heat exchange relationship with the combustionconduit for maintaining the heating z-one thereof at a controlledcombustion supporting temperature;

(3) cooling means coupled to the outlet of the combustion conduit inwhich the temperature of the gaseous product received from the heatingzone is cooled;

(a) condensate removal means integral with the cooling means whereincondensate is separated from the cooled gaseous product; and

(4) carbon dioxide detection means coupled to said cooling means forquantitatively indicating the carbon dioxide in the gaseous product fromthe heating zone;

said oxygen flow control means, combustion conduit, cooling means, andcarbon dioxide detection means being coupled in the order specified bysuitable interconnecting conduits to provide a continuous gas train.

7. An apparatus for rapidly determining the total carbon content of anaqueous system containing a small amount of a highly dispersedcarbonaceous matter which apparatus comprises:

(1) oxygen supply means for providing a confined,

continuous oxygen stream at a constant and predetermined rate;

(2) a combustion conduit having a heating zone in which there is agas-permeable diffusing member of a material essentially chemicallyinert to oxygen and steam at combustion supporting temperatures, saidcombustion conduit being connected with the oxygen supply means andadapted to receive sample injection means at one end, and at theopposite end, adapted to discharge the gaseous product formed in theheating zone into a confined cooling zone, and said diffusing memberbeing positioned within the heating zone of the combustion conduit atleast about /5 of the distance through the heating zone as measured fromthe oxygen inlet end thereof;

(a) sample injection means connected with the combustion conduit forrapidly injecting a small predetermined amount of the aqueous system tobe analyzed into the heating zone of the combustion conduit on theupstream side of the diffusing member;

(b) heating means in heat exchange relationship with the combustionconduit for maintaining the heating zone thereof at a controlledcombustion supporting temperature;

(3) cooling means connected to the combustion conduit in which thetemperature of the gaseous product received from the heating zone iscooled;

(a) condensate removal means integral with the cooling means whereincondensate is separated from the cooled gaseous product; and

(4) carbon dioxide detection means connected to the condensate removalmeans for quantitatively indicating the carbon dioxide in the gaseousproduct from the heating zone;

said oxygen supply means, combustion conduit, cooling means and carbondioxide detection means being connected in the order specified bysuitable interconnecting conduits to provide a gas train.

8. An apparatus as in claim 7 wherein the heating means is adapted toprovide a combustion supporting temperature within the range from about700 to about 1,100 C.

9. An apparatus as in claim 7 wherein the combustion conduit has amaximum cross-sectional area of about 7 square centimeters and a heatingzone bed volume within the range from about 20 to about 200 cubiccentimeters and the heating means is adapted to provide a combustionsupporting temperature within the range from about 700 to about 1,100 C.

10. An apparatus as in claim 7 wherein the combustion conduit has amaximum cross-sectional area of about 7 square centimeters and a heatingzone bed volume within the range from about 20 to about 200 cubiccentimeters,

the sample injection means is adapted for rapidly injecting a volume ofthe aqueous system to be analyzed which is from about 0.005 to about 0.5percent of the heating zone bed volume, and

the heating means is adapted to provide a combustion supportingtemperature within the range from about 700 to about 1,100 C.

11. An apparatus as in claim 7 wherein the oxygen supply means isadapted to provide oxygen at a constant fio'w rate within the range fromabout 1 to about 4 times the heating zone bed volume per minute,

the combustion conduit has a maximum cross-sectional area of about 7square centimeters and a heating zone bed volume within the range fromabout 20 to about 200 cubic centimeters,

the sample injection means is adapted for rapidly injecting a volume ofthe aqueous system to be analyzed which is from about 0.005 to about 0.5percent of the heating zone bed volume, and

the heating means is adapted to provide a combustion supportingtemperature within the range from about 700 to about 1,100 C.

12. An apparatus for rapidly determining the total carbon content of anaqueous system containing a small amount of a highly dispersedcarbonaceous matter which apparatus comprises:

(1) oxygen supply means for providing a confined,

continuous oxygen stream at a constant and predetermined rate;

(2) a combustion conduit which is an essentially cylindrical tube of amaterial resistant to oxygen and steam at combustion supportingtemperatures, with a maximum diameter of 3 centimeters, having a heatingzone bed volume within the range from 20 to 200 cubic centimeters,within which heating zone there is a diffusing member at least 0.5centimeter long constructed of a material essentially chemically inertto oxygen and steam at elevated combustion supporting temperatures, saidcombustion conduit being connected with the oxygen supply means andadapted to receive sample injection means at one end, and at theopposite end, adapted to discharge the gaseous product formed in theheating zone into a confined cooling zone, and said diffusing memberbeing positioned within the heating zone of the combustion conduit atleast about /5 of the distance through the heating zone as measured fromthe oxygen inlet end thereof;

(a) sample injection means connected with the combustion conduit forrapidly injecting in a direction essentially parallel to thelongitudinal axis of the combustion conduit a small predetermined amountof the aqueous system to be analyzed into the heating zone of thecombustion conduit on the upstream side of the diffusing member;

(b) heating means in heat exchange relationship with the combustionconduit for maintaining the heating zone thereof at a controlledcombustion temperature 'within the range from about 700 to about 1,100C.;

(3) cooling means connected to the combustion conduit in which thetemperature of the gaseous prodreceived from the heating zone is cooledto a temperature whereby condensate is formed;

(a) condensate removal means integral with the cooling means whereincondensate is separated from the cooled gaseous product; and

(4) carbon dioxide detection means connected to the cooling means forquantitatively indicating carbon dioxide in the gaseous product from theheating zone, which consists of a non-dispersive type, infraredanalyzer, sensitized to carbon dioxide, which analyzer produces a signalin the form of a variable voltage, which signal is fed to a low voltageamplifier and the enhanced signal is fed to a graphic recorder;

said oxygen supply means, combustion conduit, cooling means, and carbondioxide detection means being connected in the order specified bysuitable interconnecting conduits to provide a gas train.

13. An apparatus as in claim 12 wherein the combustion conduit isconstructed of siliceous material.

14. An apparatus as in claim 12 wherein the diffusing member comprisesignited asbestos fibers.

15. An apparatus as in claim 12 wherein the combustion conduit has aheating zone containing in addition to the diffusing member a platinumgauze downstream from the diffusing member.

References Cited by the Examiner UNITED STATES PATENTS 1,515,237 11/1924Yensen 23230 2,417,321 3/1947 Park et al. 250-435 2,555,327 6/1951Elliott 25043.5 2,698,390 12/1954 Liston 25043.5

RALPH G. NILSON, Primary Examiner.

W. F. LINDQUIST, Assistant Examiner.

1. A METHOD FOR RAPIDLY DETERMINING THE TOTAL CARBON CONTENT OF ANAQUEOUS SYSTEM CONTAINING A SMALL AMOUNT OF HIGHLY DISPERSEDCARBONACEOUS MATTER WHICH METHOD COMPRISES (1) PASSING A CONTINUOUSSTREAM OF OXYGEN AT A CONSTANT FLOW RATE THROUGH A COMBUSTION CONDUITHAVING A HEATED ZONE AT A TEMPERATURE WITHIN THE RANGE FROM ABOUT 700*TO ABOUT 1,100*C., WITHIN WHICH HEATED ZONE THERE IS POSITIONED AGAS-PERMEABLE DIFFUSING MEMBER AT A DISTANCE INTO THE HEATD ZONE FROMTHE INLET END THEREOF SUFFICIENT TO DFINE, IN COMBINATION WITH THECOMBUSTION CONDUIT, A SAMPLE EXPANSION ZONE WITHIN THE HEATED ZONE OFADEQUATE VOLUME TO AVOID THE FORMATION OF CONDENSATE UPSTREAM FROM THEHEATED ZONE, SAID DIFFUSING MEMBER BEING OF A MATERIAL WHICH ISESSENTIALLY CHEMICALLY INERT TO OXYGEN AND STEAM AT THE TEMPERATURE OFTHE HEATED ZONE; (2) RAPIDLY INJECTING A SMALL PREDETERMINED AMOUNT OFTHE AQUEOUS SYSTEM TO BE ANALYZED INTO THE OXYGEN STREAM WITHIN THEHEATED ZONE OF THE COMBUSTION CONDUIT ON THE UPSTREAM SIDE OF THEDIFFUSING MEMBER; (3) SWEEPING THE GASEOUS SIDE OF THE DIFFUSING MEMBER;ZONE THROUGH THE DIFFUSING MEMBER AND INTO A COOLING ZONE BY CONTINUINGTHE OXYGEN STREAM AT THE AFORESAID CONSTANT FLOW RATE WHEREBY THEGASEOUS PRODUCT IS COOLED; (4) THENCE SWEEPING THE COOLED GASEOUSPRODUCT INTO AN ANALYZER FOR QUANTITATIVELY INDICATING THE CARBONDIOXIDE IN THE GASEOUS PRODUCT.
 6. AN APPARATUS FOR DETERMINING THETOTAL CARBON CONTENT OF AN AQUEOUS SYSTEM CONTAINING A SMALL AMOUNT OFHIGHLY DISPERSED CARBONACEOUS MATTER, WHICH APPARATUS COMPRISES: (1)OXYGEN FLOW CONTROL MEANS FOR MAINTAINING A CONFINED CONTINUOUS OXYGENSTREAM FROM A PRESSURIZED SOURCE OF SUPPLY AT A CONSTANT ANDPREDETERMINED RATE; (2) A COMBUSTION CONDUIT HAVING AN INLET AND ANOUTLET, SAID COMBUSTION CONDUIT BEING COUPLED AT THE INLET TO THE OXYGENFLOW CONTROL MEANS AND HAVING A HEATING ZONE IN WHICH THERE IS AGAS-PERMEABLE DIFFUSING MEMBER OF A MATERIAL WHICH IS ESSENTIALLYCHEMICALLY INERT TO OXYGEN AND STREM AT COMBUSTION SUPPORTINGTEMPERATURES, SAID DIFFUSING MEMBER BEING POSITIONED WITHIN THE HEATINGZONE OF THE COMBUSTION CONDUIT AT A DISTANCE FROM THE INLET THEREOFSUFFICIENT TO DEFINE IN CONJUNCTION WITH THE COMBUSTION CONDUIT A SAMPLEEXPANSION ZONE OF ADEQUATE VOLUME TO AVOID THE FORMATION OF CONDENSATEUPSTREAM FROM THE HEATING ZONE, AND SAID COMBUSTION CONDUIT BEINGADAPTED AT THE OXYGEN INLET END THEREOF TO RECEIVE SAMPLE INJECTIONMEANS FOR RAPIDLY INJECTING A SMALL PREDETERMINED AMOUNT OF THE AQUEOUSSYSTEM TO BE ANALYZED INTO THE HEATING ZONE; (A) HEATING MEANS IN HEATEXCHANGE RELATIONSHIP WITH THE COMBUSTION CONDUIT FOR MAINTAINING THEHEATING ZONE THEREOF AT A CONTROLLED COMBUSTION SUPPORTING TEMPERATURE;(3) COOLING MEANS COUPLED TO THE OUTLET OF THE COMBUSTION CONDUIT INWHICH THE TEMPERATURE OF THE GASEOUS PRODUCT RECEIVED FROM THE HEATINGZONE IS COOLED; (A) CONDENSATE REMOVAL INTEGRAL WITH THE COOLING MEANSWHEREIN CONDENSATE IS SEPARATED FROM THE COOLED GASEOUS PRODUCT; AND (4)CARBON DIOXIDE DETECTION MEANS COUPLED TO SAID COOLING MEANS FORQUANTIATIVELY INDICATING THE CARBON DIOXIDE IN THE GASEOUS PRODUCT FROMTHE HEATING ZONE; SAID OXYGEN FLOW CONTROL MEANS, COMBUSTION CONDUIT,COOLING MEANS, AND CARBON DIOXIDE DETECTION MEANS BEING COUPLED IN THEORDER SPECIFIED BY SUITABLE INTERCONNECTING CONDUITS TO PROVIDE ACONTINUOUS GAS TRAIN.